Investigating the shock histories of lunar meteorites Miller Range 090034, 090070, and 090075 using petrography,geochemistry, and micro‐FTIR spectroscopy

Fourier transform infrared (FTIR) spectroscopy and cathodoluminescence (CL) imaging techniques, combined with electron microprobe analyses, have been used to determine the physical state of feldspathic phases that have been subject to varying levels of shock in the grouped lunar meteorites Miller Range 090034, 090070, and 090075. Six feldspathic phases have been identified based on spectral, textural, and chemical properties. A specific infrared wavelength band ratio (1064/932 cm^?1 equivalent to 9.40/10.73 μm), chosen because it can distinguish between some of the feldspathic phases, can be used to estimate the pressure regimes experienced by these phases. In addition, FTIR spatial mapping capabilities allow for visual comparison of variably shocked phases within the samples. By comparing spectral and compositional data, the origin and shock history of this lunar meteorite group has been determined, with each of the shocked feldspathic phases being related to events in its geological evolution. As such, we highlight that FTIR spectroscopy can be easily employed to identify shocked feldspathic phases in lunar samples; estimate peak shock pressures; and when compared with chemical data, can be used to investigate their shock histories.     

Influence of the crystal field effect on chemical transport in Earth's mantle: Cr3+ and Ga3+ diffusion in periclase

Experiments were performed to determine concentration-dependent diffusion coefficients of Cr³⁺ and Ga³⁺ in periclase at temperatures of 1563–2273 K. Diffusion profiles measured in the quenched samples are consistent with a theoretical model in which the mobile species is a bound M³⁺-vacancy pair, and each profile was fitted to determine the binding energy and diffusion coefficient of the pair. Trivalent chromium-vacancy pairs diffuse more slowly than Ga³⁺-vacancy pairs, and with higher migration energy, 237 kJ/mol vs. 190 kJ/mol. Cation vacancies also bind less tightly to Cr³⁺ than to Ga³⁺, with average binding free energies of ?22 and ?83 kJ/mol, respectively. At all concentrations and temperatures, Cr³⁺ diffuses much more slowly than Ga³⁺, by up to two orders of magnitude. The differences between Cr³⁺ and Ga³⁺ cannot be explained by differences in ionic radius or dipole polarizability, but are consistent with the influence of the crystal field on the partially occupied 3d orbitals of Cr³⁺. The crystal field splitting stabilizes Cr³⁺ on the octahedral cation site, increasing the energy required for Cr³⁺ to exchange positions with an adjacent vacancy. It also makes Cr³⁺-vacancy pairs less favorable, with the presence of a nearest-neighbor vacancy disrupting the symmetry of the octahedral site, thus diminishing the crystal field stabilization. Trends in the diffusion of first-row divalent transition metals in periclase can also be explained by the crystal field effect. High-spin to low-spin transitions in Fe²⁺, Co²⁺ or Mn²⁺ would significantly enhance their crystal field stabilization in periclase, and if such spin transitions occur in the deep mantle, they would be expected to slow the diffusivity of these ions significantly, perhaps by several orders of magnitude.     

Quasars from the 7C survey – I. Sample selection and radio maps

We describe the selection of candidate radio-loud quasars obtained by cross-matching radio source positions from the low-frequency (151-MHz) 7C survey with optical positions from five pairs of EO POSS-I plates scanned with the Cambridge Automatic Plate-measuring Machine (APM). The sky region studied is centred at RA 10^h 28^m, Dec.+41° and covers ≈0.057 sr. We present VLA observations of the quasar candidates, and tabulate various properties derived from the radio maps. We discuss the selection criteria of the resulting '7CQ' sample of radio-loud quasars. The 70 confirmed quasars, and some fraction of the 36 unconfirmed candidates, constitute a filtered sample with the following selection criteria: 151-MHz flux density S ₁₅₁>100 mJy; POSS-I E -plate magnitude E ≈ R <20; POSS-I colour ( O E )<1.8; the effective area of the survey drops significantly below S ₁₅₁≈200 mJy. We argue that the colour criterion excludes few if any quasars, but note, on the basis of recent work by Willott et al., that the E magnitude limit probably excludes more than 50 per cent of the radio-loud quasars.     

Clustering of galaxies in a hierarchical universe – III. Mock redshift surveys

This is the third paper in a series which combines N -body simulations and semi-analytic modelling to provide a fully spatially resolved simulation of the galaxy formation and clustering processes. Here we extract mock redshift surveys from our simulations: a cold dark matter model with either Ω₀=1 ( τ CDM) or Ω₀=0.3 and Λ=0.7 (ΛCDM). We compare the mock catalogues with the northern region (CfA2N) of the Center for Astrophysics (CfA) Redshift Surveys. We study the properties of galaxy groups and clusters identified using standard observational techniques, and also the relation of these groups to real virialized systems. Most features of CfA2N groups are reproduced quite well by both models with no obvious dependence on Ω₀. Redshift‐space correlations and pairwise velocities are also similar in the two cosmologies. The luminosity functions predicted by our galaxy formation models depend sensitively on the treatment of star formation and feedback. For the particular choices of Paper I they agree poorly with the CfA survey. To isolate the effect of this discrepancy on our mock redshift surveys, we modify galaxy luminosities in our simulations to reproduce the CfA luminosity function exactly. This adjustment improves agreement with the observed abundance of groups, which depends primarily on the galaxy luminosity density, but other statistics, connected more closely with the underlying mass distribution, remain unaffected. Regardless of the luminosity function adopted, modest differences with observation remain. These can be attributed to the presence of the 'Great Wall' in the CfA2N. It is unclear whether the greater coherence of the real structure is a result of cosmic variance, given the relatively small region studied, or reflects a physical deficiency of the models.     

Tidal tails in cold dark matter cosmologies

We study the formation of tidal tails in pairs of merging disc galaxies with structural properties motivated by current theories of cold dark matter (CDM) cosmologies. In a recent study, Dubinski, Mihos & Hernquist showed that the formation of prominent tidal tails can be strongly suppressed by massive and extended dark haloes. For the large halo-to-disc mass ratio expected in CDM cosmologies their sequence of models failed to produce strong tails like those observed in many well-known pairs of interacting galaxies. In order to test whether this effect can constrain the viability of CDM cosmologies, we construct N ‐body models of disc galaxies with structural properties derived in analogy to the recent analytical work of Mo, Mao & White. With a series of self-consistent collisionless simulations of galaxy–galaxy mergers we demonstrate that even the discs of very massive dark haloes have no problems developing long tidal tails, provided the halo spin parameter is large enough. For our class of models, the halo-to-disc mass ratio is not a good indicator of the ability to produce tails. Instead, the relative size of disc and halo or, alternatively, the ratio of circular velocity to local escape speed at the half mass radius of the disc is a more useful criterion. This result holds in all CDM models. While tidal tails can provide useful information on the structure of galaxies, it thus appears unlikely that they are able to constrain the values of the cosmological parameters within these models.     

Astronomical network event and observation notification

Networks are becoming a key element in most current and all future, telescope and observatory projects. The ability to easily and efficiently pass observation data, alert data and instrumentation requests between distributed systems could enable science as never before. However, any effective large scale or meta‐network of astronomical resources will require a common communication format or development resources will have to be continuously dedicated to creating interpreters. The necessary elements of any astronomy communication can be easily identified, efficiently described and rigidly formatted so that both robotic and human operations can use the same data. In this paper we will explore the current state of notification, what notification requirements are essential to create a successful standard and present a standard now under development by the International Virtual Observatory Alliance (IVOA), called the VOEvent. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A protocol standard for heterogeneous telescope networks

The scientific need for a standard protocol permitting the exchange of generic observing services is rapidly escalating as more observatories adopt service observing as a standard operating mode and as more remote or robotic telescopes are brought on‐line. To respond to this need, we present the results of the first interoperability workshop for Heterogeneous Telescope Networks (HTN) held in Exeter. We present a draft protocol, designed to be independent of the specific instrumentation and software that controls the remote and/or robotic telescopes, allowing these telescopes to appear to the user with a unified interface despite any underlying architectural differences. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Winchcombe fireball—That lucky survivor

On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s⁻¹). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.     

The 1996 Biescas campsite disaster in the Central Spanish Pyrenees,and its temporal and spatial context

On the evening of the 7 August 1996 an intense storm occurred over the Arás catchment near Biescas in the central Pyrenees. Eighty-seven people were killed as a result of the subsequent flood, which hit a campsite located on the alluvial fan at the outlet of the 18·8 km² catchment. This paper presents the main results of a hydromorphological study of the event. The Betés subcatchment received the most intense rainfall, estimated at somewhat in excess of 250 mm, which resulted in a peak flow from this tributary of 300 m³ s⁻¹. Just downstream from the Betés river junction, flow in the main channel reached 400 m³ s⁻¹, increasing to around 500 m³ s⁻¹ further downstream. Rainfall in the larger Aso tributary was less intense, and in the head reaches flow remained within-bank, representing a one in two-year return period event. Flow from this tributary did not exceed 100 m³ s⁻¹, indicating that the Betés subcatchment supplied some 75% of the flow from just 28·7% of the catchment area. The extreme flows caused the collapse of a series of sediment trap dams in the Arás channel downstream of the Betés junction. This resulted in the addition of 68 000 m³ of sediment to an already disastrous event. Data from other rain gauges in the area showed both the extremely local nature of the event, and the problems of return period analysis for such storms, whose peaks are rarely observed at gauges. Together with the high geomorphological risks of the zone, this leads to the conclusion that a new method of spatial and temporal risk analysis is required for infrastructure planning. © 1997 John Wiley & Sons, Ltd.     

Characterizing spatiotemporal trends in extreme precipitation in Southeast Texas

Natural Hazards - Rainfall extreme value analysis provides information that has been crucial in characterizing risk, designing successful infrastructure systems, and ultimately protecting people...